Liquid crystal (LCD) is a material between liquid and crystal, the display principle is that different voltages are applied to the liquid crystals to change the state of the molecular arrangement, thereby controlling the through-put of light rays to display various images. The liquid crystal does not emit light per se. Instead, it controls allowing the light rays to pass through or not. Therefore, all liquid crystal display modules (LCD module) need backlight sources for illumination.
In the past, the backlight source used in the LCD module is mainly a cold cathode fluorescent lamp (CCFL). As the development of the liquid crystal technique, light emitting diodes (LEDs) start to be wildly used in the LED modules as the backlight sources. As the LED is used as the backlight source, power consumption can be significantly reduced, a contrast and gray-scale number of the displayed picture can be promoted, and a ghost shadow can be decreased. The technical superiority is quite evident.
Local dimming is a technique enabling the LCD module to achieve different degrees of luminance and lighting variance in different sections. It generally includes three types, which are respectively 0 dimensional (0D), 1 dimensional (1D) and 2 dimensional (2D) luminance control, and respectively correspond to the backlight sources including a flat light source (e.g. Flat Fluorescent; FFL and OLED), a CCFL (or an external electrode fluorescent lamp; EEFL similar to CCFL) and an LED.
Currently, LED is the best light source among the backlight sources to achieve the optimal control of the local dimming. This it because the light emitting manner of the flat light source is to lighten the whole plane or darken the whole plane, the backlight cannot be varied for small sections in various brightness. CCFL or EEFL is a line light source, and the speed of turning on and off is not fast enough. If the switching speed is driven forcibly, the lifetime of the CCFL will be reduced. A direct-lit LED backlight source uses multiple pieces (for example, a certain type of 46-inch LCD TV uses about 1500 white LEDs), and the pieces are arranged in an array, each LED can be theoretically considered as a small unit for local control, and therefore is very advantageous for implementing the local dimming technique.
However, there still exist some drawbacks for the direct-lit LED backlight source to implement the local dimming. The main reason is that, in the LED backlight source, the LED array is arranged directly under an LCD glass to provide the light source to the LCD glass, so as to accomplish the dimming of each section. However, such a manner needs a great amount of LEDs, the power consumption is high, and the thickness is thicker. A subsequently developed LED edge-lit technique also has problems that the local dimming controlled sections are fewer since the local dimming of fewer sections can be achieved by only two light bars. In addition, the lights of the sections will be influenced by each other. The liquid crystal displaying quality will be affected to some extent.
Therefore, it is necessary to provide a liquid crystal display module with an improved local dimming effect to solve the existing problems of the current technique.